Solid oxide fuel cell device

ABSTRACT

A fuel cell device including an elongate ceramic substrate having an exterior surface defining an interior ceramic support structure having non-active end regions and an active zone therebetween that includes electrodes in opposing relation with an electrolyte therebetween for undergoing a fuel cell reaction when supplied with heat, fuel and oxidizer. The electrolyte is a ceramic co-fired with the interior ceramic support structure. The end regions lack opposing electrodes and extend away from the active zone to dissipate heat. Gas inlets are positioned in the end regions with respective outlets in either the active zone or opposite end region, and elongate passages are coupled therebetween at least partially extending in opposing relation through the active zone. The electrodes are positioned adjacent the gas passages in the active zone and are electrically connected to exterior contact surfaces on the exterior surface of the end regions for external connection to voltage nodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Pat. No. 8,153,318 issuedApr. 10, 2012, and entitled METHOD OF MAKING A FUEL CELL DEVICE., whichis a continuation of U.S. Pat. No. 7,981,565 issued Jul. 19, 2011, andentitled SOLID OXIDE FUEL CELL DEVICE AND SYSTEM, the disclosures ofwhich are incorporated herein by reference in their entirety as ifcompletely set forth herein below.

FIELD OF THE INVENTION

This invention relates to solid oxide fuel cell devices and systems, andmethods of manufacturing the devices, and more particularly, to a solidoxide fuel cell device in the form of a multi-layer monolithic SOFCStick™.

BACKGROUND OF INVENTION

Ceramic tubes have found a use in the manufacture of Solid Oxide FuelCells (SOFCs). There are several types of fuel cells, each offering adifferent mechanism of converting fuel and air to produce electricitywithout combustion. In SOFCs, the barrier layer (the “electrolyte”)between the fuel and the air is a ceramic layer, which allows oxygenatoms to migrate through the layer to complete a chemical reaction.Because ceramic is a poor conductor of oxygen atoms at room temperature,the fuel cell is operated at 700° C. to 1000° C., and the ceramic layeris made as thin as possible.

Early tubular SOFCs were produced by the Westinghouse Corporation usinglong, fairly large diameter, extruded tubes of zirconia ceramic. Typicaltube lengths were several feet long, with tube diameters ranging from ¼inch to ½ inch. A complete structure for a fuel cell typically containedroughly ten tubes. Over time, researchers and industry groups settled ona formula for the zirconia ceramic which contains 8 mol % Y₂O₃. Thismaterial is made by, among others, Tosoh of Japan as product TZ-8Y.

Another method of making SOFCs makes use of flat plates of zirconia,stacked together with other anodes and cathodes, to achieve the fuelcell structure. Compared to the tall, narrow devices envisioned byWestinghouse, these flat plate structures can be cube shaped, 6 to 8inches on an edge, with a clamping mechanism to hold the entire stacktogether.

A still newer method envisions using larger quantities of small diametertubes having very thin walls. The use of thin walled ceramic isimportant in SOFCs because the transfer rate of oxygen ions is limitedby distance and temperature. If a thinner layer of zirconia is used, thefinal device can be operated at a lower temperature while maintainingthe same efficiency. Literature describes the need to make ceramic tubesat 150 μm or less wall thickness.

There are several main technical problems that have stymied thesuccessful implementation of SOFCs. One problem is the need to preventcracking of the ceramic elements during heating. For this, the tubularSOFC approach is better than the competing “stack” type (made fromlarge, flat ceramic plates) because the tube is essentiallyone-dimensional. The tube can get hot in the middle, for example, andexpand but not crack. For example, a tube furnace can heat a 36″ longalumina tube, 4″ in diameter, and it will become red hot in the center,and cold enough to touch at the ends. Because the tube is heated evenlyin the center section, that center section expands, making the tubebecome longer, but it does not crack. A ceramic plate heated in thecenter only would quickly break into pieces because the center expandswhile the outside remains the same size. The key property of the tube isthat it is uniaxial, or one-dimensional.

A second key challenge is to make contact to the SOFC. The SOFC ideallyoperates at high temperature (typically 700-1000° C.), yet it also needsto be connected to the outside world for air and fuel, and also to makeelectrical connection. Ideally, one would like to connect at roomtemperature. Connecting at high temperature is problematic becauseorganic material cannot be used, so one must use glass seals ormechanical seals. These are unreliable, in part, because of expansionproblems. They can also be expensive.

Thus, previous SOFC systems have difficulty with at least the twoproblems cited above. The plate technology also has difficulty with theedges of the plates in terms of sealing the gas ports, and hasdifficulty with fast heating, as well as cracking. The tube approachresolves the cracking issue but still has other problems. An SOFC tubeis useful as a gas container only. To work it must be used inside alarger air container. This is bulky. A key challenge of using tubes isthat you must apply both heat and air to the outside of the tube; air toprovide the O₂ for the reaction, and heat to accelerate the reaction.Usually, the heat would be applied by burning fuel, so instead ofapplying air with 20% O₂ (typical), the air is actually partiallyreduced (partially burned to provide the heat) and this lowers thedriving potential of the cell.

An SOFC tube is also limited in its scalability. To achieve greater kVoutput, more tubes must be added. Each tube is a single electrolytelayer, such that increases are bulky. The solid electrolyte tubetechnology is further limited in terms of achievable electrolytethinness. A thinner electrolyte is more efficient. Electrolyte thicknessof 2 μm or even 1 μm would be optimal for high power, but is verydifficult to achieve in solid electrolyte tubes. It is noted that asingle fuel cell area produces about 0.5 to 1 volt (this is inherent dueto the driving force of the chemical reaction, in the same way that abattery gives off 1.2 volts), but the current, and therefore the power,depend on several factors. Higher current will result from factors thatmake more oxygen ions migrate across the electrolyte in a given time.These factors are higher temperature, thinner electrolyte, and largerarea.

SUMMARY OF THE INVENTION

The invention provides a solid oxide fuel cell device comprising anelongate ceramic substrate having an exterior surface defining aninterior ceramic support structure having a first non-active end regionadjacent a first end, a second non-active end region adjacent a secondend, and an active zone between the first and second non-active endregions. The active zone comprises an anode and a cathode in opposingrelation with an electrolyte therebetween for undergoing a fuel cellreaction when supplied with heat, fuel and oxidizer, and the first andsecond non-active end regions lack the anode and cathode in opposingrelation and extend away from the active zone without being heated todissipate heat and to thereby remain at a lower temperature than theactive zone when the active zone is supplied with heat. The devicefurther comprises a fuel inlet in the first non-active end region forreceiving the supply of fuel and a respective fuel outlet in at leastone of the active zone or the second non-active end region, the fuelinlet and the fuel outlet coupled therebetween by an elongate fuelpassage at least partially extending through the active zone within theinterior ceramic support structure, wherein the anode is adjacent thefuel passage in the active zone within the interior ceramic supportstructure and electrically connected from within the interior ceramicsupport structure to a first exterior contact surface on the exteriorsurface of the elongate ceramic substrate in at least one of the firstor second non-active end regions for external connection to a negativevoltage node. Similarly, the device comprises an oxidizer inlet in thesecond non-active end region for receiving the supply of oxidizer and arespective oxidizer outlet in at least one of the active zone or thefirst non-active end region, the oxidizer inlet and the oxidizer outletcoupled therebetween by an elongate oxidizer passage at least partiallyextending through the active zone within the interior ceramic supportstructure in opposing relation to the elongate fuel passage, wherein thecathode is adjacent the oxidizer passage in the active zone within theinterior ceramic support structure and electrically connected fromwithin the interior ceramic support structure to a second exteriorcontact surface on the exterior surface of the elongate ceramicsubstrate in at least one of the first or second non-active end regionsfor external connection to a positive voltage node. The electrolyte is aceramic that is co-fired with the interior ceramic support structure.

BRIEF DESCRIPTION OF THE INVENTION

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIGS. 1 and 1A depict, in side cross-sectional view and topcross-sectional view, respectively, one embodiment of a basic SOFCStick™ device of the invention, having a single anode layer, cathodelayer and electrolyte layer, and a hot zone between two end cold zones.

FIG. 2 depicts in perspective view a first end of one embodiment of aSOFC Stick™ device of the invention with a fuel supply tube connectedthereto.

FIG. 3A depicts in perspective view a SOFC Stick™ device according toone embodiment of the invention, but having modified ends.

FIG. 3B depicts in perspective view a fuel supply tube connected to onemodified end of the device of FIG. 3A.

FIG. 4A depicts in perspective view a metallurgical bonding attachmentmeans to a plurality of SOFC Stick™ devices to make electricalconnection to positive and negative voltage nodes according to oneembodiment of the invention.

FIG. 4B depicts in schematic end view a connection between multiple SOFCStick™ devices according to one embodiment of the invention, where eachSOFC Stick™ device includes a plurality of anodes and cathodes.

FIG. 5 depicts in schematic end view a mechanical attachment means formaking the electrical connection to positive and negative voltage nodesaccording to one embodiment of the invention.

FIGS. 6A and 6B depict in perspective views an alternative embodimenthaving a single cold zone at one end of a SOFC Stick™ device to whichfuel and air supply tubes are attached, with the other end being in thehot zone.

FIGS. 7A and 7B are cross-sectional side and top views, respectively,illustrating a plurality of support pillars in the air and fuel passagesaccording to one embodiment of the invention.

FIGS. 7C and 7D are micrographs depicting the use of spherical balls inthe fuel and air passages as the support pillars according to anotherembodiment of the invention.

FIG. 8A depicts in cross-section one embodiment of the inventioncontaining two fuel cells connected externally in parallel.

FIG. 8B depicts in cross-sectional view another embodiment of theinvention similar to FIG. 8A, but having the two fuel cells connectedinternally in parallel through the use of vias.

FIGS. 9A and 9B depict in cross-sectional views a multi-fuel cell designaccording to an embodiment of the invention having shared anodes andcathodes, where FIG. 9A depicts three fuel cell layers connected inparallel and FIG. 9B depicts three fuel cells connected in series.

FIG. 10 depicts in schematic side view an SOFC Stick™ device accordingto one embodiment of the invention having a fuel supply tube connectedto a cold end of the device and a side of the device open in the hotzone to an air passage for supply of heated air to the device in the hotzone.

FIG. 10A depicts in schematic side view a variation of the embodiment ofFIG. 10, where the hot zone is positioned between opposing cold ends.

FIG. 10B depicts the SOFC Stick™ device of FIG. 10A in topcross-sectional view taken along line 10B-10B.

FIGS. 11-24 schematically depict various embodiments of the invention,where FIG. 11 provides a key for the components depicted in FIGS. 12-24.

FIGS. 25A and 27A depict in schematic top plan view and FIG. 27B depictsin schematic side view an SOFC Stick™ device according to one embodimentof the invention having a panhandle design with an elongate section atone cold end and a large surface area section at the opposing hot end.

FIGS. 25B and 26A depict in schematic top plan view and FIG. 26B depictsin schematic side view an alternative embodiment of the panhandle designhaving two elongate sections at opposing cold ends with a center largesurface area section in a central hot zone.

FIGS. 28A-28D depict an SOFC Stick™ device according to one embodimentof the invention, having a spiral or rolled, tubular configuration,where FIGS. 28A-28C depict the unrolled structure in schematic top view,end view and side view, respectively, and FIG. 28D depicts the spiral orrolled, tubular configuration in schematic perspective view.

FIGS. 29A-29G depict another alternative embodiment of the inventionwherein the SOFC Stick™ device has a tubular concentric form, and whereFIG. 29A depicts the device in schematic isometric view, FIGS. 29B-29Edepict cross-sectional views taken from FIG. 29A, FIG. 29F depicts anend view at the air input end, and FIG. 29G depicts an end view at thefuel input end.

FIG. 30A depicts in schematic cross-sectional side view an embodiment ofan SOFC Stick™ device of the invention having an integrated pre-heatzone preceding an active zone in the hot zone, and FIGS. 30B and 30Cdepict the device of FIG. 30A in schematic cross-sectional view takenalong lines 30B-30B and 30C-30C, respectively.

FIGS. 31A-31C are similar to FIGS. 30A-30C, but depict two cold zoneswith a central hot zone.

FIGS. 32A-32B depict in schematic cross-sectional side view andschematic cross-sectional top view taken along line 32B-32B of FIG. 32A,respectively, an embodiment similar to that depicted in FIGS. 31A-31C,but further including pre-heat chambers extending between the fuel inletand the fuel passage and between the air inlet and the air passage, eachpre-heat chamber extending from the cold zone into the pre-heat zone ofthe hot zone.

FIGS. 33A-33C depict another embodiment of the invention for pre-heatingthe air and fuel, where FIG. 33A is a schematic cross-sectional sideview through the longitudinal center of the SOFC Stick™ device, FIG. 33Bis a schematic cross-sectional top view taken along line 33B-33B of FIG.33A, and FIG. 33C is a schematic cross-sectional bottom view taken alongline 33C-33C of FIG. 33A.

FIGS. 34A and 34B depict in schematic oblique front view and schematicside view, respectively, an embodiment of the invention having multipleanodes and cathodes interconnected externally in series.

FIG. 35 depicts in schematic side view the structure of FIG. 34B doubledwith the two structures connected externally by metal stripes to providea series-parallel design.

FIGS. 36A and 36B depict in schematic side view and perspective viewanother embodiment of the invention including metal stripes to connectanodes and cathodes in series and/or parallel in the hot zone and longmetal stripes extending from the hot zone to the cold zone for makinglow temperature connection in the cold zones to the positive andnegative voltage nodes.

FIG. 37 depicts in schematic isometric view an embodiment similar tothat of FIG. 36B, but having a single cold zone for the air and fuelsupply connections and for the voltage node connection.

FIGS. 38A and 38B depict in schematic cross-sectional side view anembodiment of the invention having multiple exit gaps along the sides ofthe device for bake-out of organic material used to form passages withinthe structure.

FIG. 39 depicts in schematic cross-sectional end view another embodimentof the invention in which anode material is used as the supportingstructure, referred to as an anode-supported version of an SOFC Stick™device.

FIGS. 40A and 40B depict in schematic cross-sectional end view andschematic cross-sectional side view, respectively, an anode-supportedversion according to another embodiment of an SOFC Stick™ device of theinvention in which an open fuel passage is eliminated in favor of aporous anode that serves the function of conveying the fuel through thedevice.

FIGS. 41A and 41B depict in schematic cross-sectional end view andschematic cross-sectional top view, respectively, another embodiment ofan anode-supported version of an SOFC Stick™ device of the invention, inwhich multiple air passages are provided within the anode-supportingstructure, and a single fuel passage is provided normal to the multipleair passages.

FIGS. 42A-42C depict in schematic cross-sectional view a method forforming an electrode layer in a passage of an SOFC Stick™ device of theinvention, according to one embodiment.

FIG. 43 depicts in schematic cross-sectional side view anotherembodiment of the invention in which the electrolyte layer is providedwith an uneven topography to increase the surface area available toreceive an electrode layer.

FIG. 44 depicts in schematic cross-sectional side view an alternativeembodiment of the invention for providing uneven topography on theelectrolyte layer.

FIG. 45A depicts in schematic top view and FIG. 45B depicts incross-sectional view through the hot zone an embodiment of an SOFCStick™ device of the invention having a plurality of fuel cells on eachof a left and right side of the device, with a bridging portiontherebetween.

FIGS. 46A and 46B depict in schematic perspective view and schematiccross-sectional view, respectively, another embodiment of an SOFC Stick™device of the invention having large exterior contact pads to provide alarge or wide path of low resistance for electrons to travel to the coldend of the device.

FIG. 47 depicts in schematic cross-sectional side view an SOFC Stick™device according to another embodiment of the invention having a singleexhaust passage for both spent fuel and air.

FIGS. 48A-48C depict an alternative embodiment referred to as an“end-rolled SOFC Stick™ device” having a thick portion and a thin rolledportion, wherein FIG. 48A depicts the unrolled device in perspectiveview, FIG. 48B depicts the rolled device in cross-sectional side view,and FIG. 48C depicts the rolled device in perspective view.

DETAILED DESCRIPTION

In one embodiment, the invention provides a SOFC device and system inwhich the fuel port and the air port are made in one monolithicstructure. In one embodiment, the SOFC device is an elongate structure,essentially a relatively flat or rectangular stick (and thus, referredto as a SOFC Stick™ device), in which the length is considerably greaterthan the width or thickness. The SOFC Stick™ devices are capable ofhaving cold ends while the center is hot (cold ends being <300° C.; hotcenter being >400° C., and most likely >700° C.). Slow heat conductionof ceramic can prevent the hot center from fully heating the colderends. In addition, the ends are quickly radiating away any heat thatarrives there. The invention includes the realization that by havingcold ends for connection, it is possible to make easier connection tothe anode, cathode, fuel inlet and H₂O CO₂ outlet, and air inlet and airoutlet. While tubular fuel cell constructions are also capable of havingcold ends with a hot center, the prior art does not take advantage ofthis benefit of ceramic tubes, but instead, places the entire tube inthe furnace, or the hot zone, such that high temperature connectionshave been required. The prior art recognizes the complexity and cost ofmaking high temperature brazed connections for the fuel input, but hasnot recognized the solution presented herein. The SOFC Stick™ device ofthe invention is long and skinny so that it has the thermal propertyadvantages discussed above that allow it to be heated in the center andstill have cool ends. This makes it structurally sound with temperature,and makes it relatively easy to connect fuel, air and electrodes. TheSOFC Stick™ device is essentially a stand-alone system, needing onlyheat, fuel, and air to be added in order to make electricity. Thestructure is designed so that these things can be readily attached.

The SOFC Stick™ device of the invention is a multi-layer structure andmay be made using a multi-layer co-fired approach, which offers severalother advantages. First, the device is monolithic, which helps to makeit structurally sound. Second, the device lends itself to traditionalhigh volume manufacturing techniques such as those used in MLCC(multi-layer co-fired ceramic) production of capacitor chips. (It isbelieved that multi-layer capacitor production is the largest volume useof technical ceramics, and the technology is proven for high volumemanufacturing.) Third, thin electrolyte layers can be achieved withinthe structure at no additional cost or complexity. Electrolyte layers of2 μm thickness are possible using the MLCC approach, whereas it is hardto imagine a SOFC tube with less than a 60 μm electrolyte wallthickness. Hence, the SOFC Stick™ device of the invention can be about30 times more efficient than a SOFC tube. Finally, the multi-layer SOFCStick™ devices of the invention could each have many hundreds, orthousands, of layers, which would offer the largest area and greatestdensity.

Consider the surface area of a SOFC tube of the prior art versus a SOFCStick™ device of the invention. For example, consider a 0.25″ diametertube versus a 0.25″×0.25″ SOFC Stick™ device. In the tube, thecircumference is 3.14×D, or 0.785″. In the 0.25″ SOFC Stick™ device, theusable width of one layer is about 0.2 inch. Therefore, it takes about 4layers to give the same area as one tube. These figures are dramaticallydifferent than those for capacitor technology. The state of the art forJapanese multi-layer capacitors is currently 600 layers of 2 μmthicknesses. The Japanese will likely soon launch 1000 layer parts inproduction, and they make them now in the laboratory. These chipcapacitors with 600 layers are only 0.060″ (1500 μm). Applying thismanufacturing technology to a SOFC Stick™ device of the invention, in a0.25″ device having a 2 μm electrolyte thickness and air/fuel passageswith respective cathodes/anodes of 10 μm thickness, it would be feasibleto produce a single device with 529 layers. That would be the equivalentof 132 tubes. Prior art strategies either add more tubes, increasediameter, and/or increase tube length to get more power, with resultbeing very large structures for high power output. The invention, on theother hand, either adds more layers to a single SOFC Stick™ device toget more power and/or uses thinner layers or passages in the device,thereby enabling miniaturization for SOFC technology. Moreover, thebenefit in the present invention is a squared effect, just like incapacitors. When the electrolyte layers are made half as thick, thepower doubles, and then you can fit more layers in the device so powerdoubles again.

Another key feature of the invention is that it would be easy to linklayers internally to increase the output voltage of the SOFC Stick™device. Assuming 1 volt per layer, 12 volts output may be obtained bythe SOFC Stick™ devices of the invention using via holes to link groupsof 12 together. After that, further connections may link groups of 12 inparallel to achieve higher current. This can be done with existingmethods used in capacitor chip technology. The critical difference isthat the invention overcomes the brazing and complex wiring that othertechnologies must use.

The invention also provides a greater variety of electrode optionscompared to the prior art. Precious metals will work for both the anodesand cathodes. Silver is cheaper, but for higher temperature, a blendwith Pd, Pt, or Au would be needed, with Pd possibly being the lowestpriced of the three. Much research has focused on non-precious metalconductors. On the fuel side, attempts have been made to use nickel, butany exposure to oxygen will oxidize the metal at high temperature.Conductive ceramics are also known, and can be used in the invention. Inshort, the present invention may utilize any sort ofanode/cathode/electrolyte system that can be sintered.

In an embodiment of the invention, it is possible that when a large areaof 2 μm tape is unsupported, with air/gas on both sides, the layer mightbecome fragile. It is envisioned to leave pillars across the gap. Thesewould look something like pillars in caves where a stalactite andstalagmite meet. They could be spaced evenly and frequently, giving muchbetter strength to the structure.

For attachment of the gas and air supply, it is envisioned that the endtemperature is below 300° C., for example, below 150° C., such that hightemperature flexible silicone tubes or latex rubber tubes, for example,may be used to attach to the SOFC Stick™ devices. These flexible tubescan simply stretch over the end of the device, and thereby form a seal.These materials are available in the standard McMaster catalog. Siliconeis commonly used at 150° C. or above as an oven gasket, without losingits properties. The many silicone or latex rubber tubes of a multi-stickSOFC Stick™ system could be connected to a supply with barb connections.

The anode material or the cathode material, or both electrode materials,may be a metal or alloy. Suitable metals and alloys for anodes andcathodes are known to those of ordinary skill in the art. Alternatively,one or both electrode materials may be an electronically conductivegreen ceramic, which are also known to those of ordinary skill in theart. For example, the anode material may be a partially sinteredmetallic nickel coated with yttria-stabilized zirconia, and the cathodematerial may be a modified lanthanum manganite, which has a perovskitestructure.

In another embodiment, one or both of the electrode materials may be acomposite of a green ceramic and a conductive metal present in an amountsufficient to render the composite conductive. In general, a ceramicmatrix becomes electronically conductive when the metal particles startto touch. The amount of metal sufficient to render the composite matrixconductive will vary depending mainly on the metal particle morphology.For example, the amount of metal will generally need to be higher forspherical powder metal than for metal flakes. In an exemplaryembodiment, the composite comprises a matrix of the green ceramic withabout 40-90% conductive metal particles dispersed therein. The greenceramic matrix may be the same or different than the green ceramicmaterial used for the electrolyte layer.

In the embodiments in which one or both electrode materials include aceramic, i.e., the electronically conductive green ceramic or thecomposite, the green ceramic in the electrode materials and the greenceramic material for the electrolyte may contain cross-linkable organicbinders, such that during lamination, the pressure is sufficient tocross-link the organic binder within the layers as well as to linkpolymer molecular chains between the layers.

Reference will now be made to the drawings in which like numerals areused throughout to refer to like components. Reference numbers used inthe Figures are as follows:

-   -   10 SOFC Stick™ device    -   11 a First end    -   11 b Second end    -   12 Fuel inlet    -   13 Fuel pre-heat chamber    -   14 Fuel passage    -   16 Fuel outlet    -   18 Air inlet    -   19 Air pre-heat chamber    -   20 Air passage    -   21 Exhaust passage    -   22 Air outlet    -   24 Anode layer    -   25 Exposed anode portion    -   26 Cathode layer    -   27 Exposed cathode portion    -   28 Electrolyte layer    -   30 Cold zone (or second temperature)    -   31 Transition zone    -   32 Hot zone (or heated zone or first temperature zone)    -   33 a Pre-heat zone    -   33 b Active zone    -   34 Fuel supply    -   36 Air supply    -   38 Negative voltage node    -   40 Positive voltage node    -   42 Wire    -   44 Contact pad    -   46 Solder connection    -   48 Spring clip    -   50 Supply tube    -   52 Tie wrap    -   54 Ceramic pillars    -   56 First via    -   58 Second via    -   60 Barrier coating    -   62 Surface particles    -   64 Textured surface layer    -   66 Anode suspension    -   70 Openings    -   72 Organic material    -   80 Left side    -   82 Right side    -   84 Bridging portion    -   90 Bridge    -   100 SOFC Stick™ device    -   102 Elongate section    -   104 Large surface area section    -   106 Elongate section    -   200 Spiral Tubular SOFC Stick™ device    -   300 Concentric Tubular SOFC Stick™ device    -   400 End-rolled SOFC Stick™ device    -   402 Thick portion    -   404 Thin portion

FIGS. 1 and 1A depict, in side cross-sectional view and topcross-sectional view, respectively, one embodiment of a basic SOFCStick™ device 10 of the invention, having a single anode layer 24,cathode layer 26 and electrolyte layer 28, wherein the device ismonolithic. The SOFC Stick™ device 10 includes a fuel inlet 12, a fueloutlet 16 and a fuel passage 14 therebetween. Device 10 further includesan air inlet 18, an air outlet 22 and an air passage 20 therebetween.The fuel passage 14 and the air passage 20 are in an opposing andparallel relation, and the flow of fuel from fuel supply 34 through thefuel passage 14 is in a direction opposite to the flow of air from airsupply 36 through air passage 20. The electrolyte layer 28 is disposedbetween the fuel passage 14 and the air passage 20. The anode layer 24is disposed between the fuel passage 14 and the electrolyte layer 28.Similarly, the cathode layer 26 is disposed between the air passage 20and the electrolyte layer 28. The remainder of the SOFC Stick™ device 10comprises ceramic 29, which may be of the same material as theelectrolyte layer 28 or may be a different but compatible ceramicmaterial. The electrolyte layer 28 is considered to be that portion ofthe ceramic lying between opposing areas of the anode 24 and cathode 26,as indicated by dashed lines. It is in the electrolyte layer 28 thatoxygen ions pass from the air passage to the fuel passage. As shown inFIG. 1, O₂ from the air supply 36 travels through the air passage 20 andis ionized by the cathode layer 26 to form 2O⁻, which travels throughthe electrolyte layer 28 and through the anode 24 into the fuel passage14 where it reacts with fuel, for example, a hydrocarbon, from the fuelsupply 34 to first form CO and H₂ and then to form H₂O and CO₂. WhileFIG. 1 depicts the reaction using a hydrocarbon as the fuel, theinvention is not so limited. Any type of fuel commonly used in SOFCs maybe used in the present invention. Fuel supply 34 may be any hydrocarbonsource or hydrogen source, for example. Methane (CH₄), propane (C₃H₈)and butane (C₄H₁₀) are examples of hydrocarbon fuels.

For the reaction to occur, heat must be applied to the SOFC Stick™device 10. In accordance with the invention, the length of the SOFCStick™ device 10 is long enough that the device can be divided into ahot zone 32 (or heated zone) in the center of the device and cold zones30 at each end 11 a and 11 b of the device 10. Between the hot zone 32and the cold zones 30, a transition zone 31 exists. The hot zone 32 willtypically operate above 400° C. In exemplary embodiments, the hot zone32 will operate at temperatures>600° C., for example >700° C. The coldzones 30 are not exposed to a heat source, and due to the length of theSOFC Stick™ device 10 and the thermal property advantages of the ceramicmaterials, heat dissipates outside the hot zone, such that the coldzones 30 have a temperature<300° C. It is believed that heat transferfrom the hot zone down the length of the ceramic to the end of the coldzone is slow, whereas the heat transfer from the ceramic materialoutside the heat zone into the air is relatively faster. Thus, most ofthe heat inputted in the hot zone is lost to the air (mainly in thetransition zone) before it can reach the end of the cold zone. Inexemplary embodiments of the invention, the cold zones 30 have atemperature<150° C. In a further exemplary embodiment, the cold zones 30are at room temperature. The transition zones 31 have temperaturesbetween the operating temperature of the hot zone 32 and the temperatureof the cold zones 30, and it is within the transition zones 31 that thesignificant amount of heat dissipation occurs.

Because the dominant coefficient of thermal expansion (CTE) is along thelength of the SOFC Stick™ device 10, and is therefore essentiallyone-dimensional, fast heating of the center is permitted withoutcracking. In exemplary embodiments, the length of the device 10 is atleast 5 times greater than the width and thickness of the device. Infurther exemplary embodiments, the length of the device 10 is at least10 times greater than the width and thickness of the device. In yetfurther exemplary embodiments, the length of the device 10 is at least15 times greater than the width and thickness of the device. Inaddition, in exemplary embodiments, the width is greater than thethickness, which provides for greater area. For example, the width maybe at least twice the thickness. By way of further example, a 0.2 inchthick SOFC Stick™ device 10 may have a width of 0.5 inch. It may beappreciated that the drawings are not shown to scale, but merely give ageneral idea of the relative dimensions.

In accordance with the invention, electrical connections to the anodeand cathode are made in the cold zones 30 of the SOFC Stick™ device 10.In an exemplary embodiment, the anode 24 and the cathode 26 will each beexposed to an outer surface of the SOFC Stick™ device 10 in a cold zone30 to allow an electrical connection to be made. A negative voltage node38 is connected via a wire 42, for example, to the exposed anode portion25 and a positive voltage node 40 is connected via a wire 42, forexample, to the exposed cathode portion 27. Because the SOFC Stick™device 10 has cold zones 30 at each end 11 a, 11 b of the device, lowtemperature rigid electrical connections can be made, which is asignificant advantage over the prior art, which generally requires hightemperature brazing methods to make the electrical connections.

FIG. 2 depicts in perspective view a first end 11 a of SOFC Stick™device 10 with a supply tube 50 attached over the end and secured with atie wrap 52. Fuel from fuel supply 34 will then be fed through thesupply tube 50 and into the fuel inlet 12. As a result of first end 11 abeing in the cold zone 30, flexible plastic tubing or other lowtemperature type connection material may be used to connect the fuelsupply 34 to the fuel inlet 12. The need for high temperature brazing tomake the fuel connection is eliminated by the invention.

FIG. 3A depicts in perspective view a SOFC Stick™ device 10 similar tothat depicted in FIG. 1, but having modified first and second ends 11 a,11 b. Ends 11 a, 11 b have been machined to form cylindrical endportions to facilitate connection of the fuel supply 34 and air supply36. FIG. 3B depicts in perspective view a supply tube 50 connected tothe first end 11 a for feeding fuel from fuel supply 34 to the fuelinlet 12. By way of example, supply tube 50 can be a silicone or latexrubber tube that forms a tight seal by virtue of its elasticity to thefirst end 11 a. It may be appreciated that the flexibility andelasticity of the supply tubes 50 can provide a shock-absorbing holderfor the SOFC Stick™ devices when the use is in a mobile device subjectto vibrations. In the prior art, the tubes or plates were rigidlybrazed, and thus subject to crack failure if used in a dynamicenvironment. Therefore, the additional function of the supply tubes 50as vibration dampers offers a unique advantage compared to the priorart.

Referring back to FIG. 3A, contact pads 44 are provided on the outersurface of the SOFC Stick™ device 10 so as to make contact with theexposed anode portion 25 and the exposed cathode portion 27. Materialfor the contact pads 44 should be electrically conductive so as toelectrically connect the voltage nodes 38, 40 to their respective anode24 and cathode 26. It may be appreciated that any suitable method may beused for forming the contact pads 44. For example, metal pads may beprinted onto the outer surface of a sintered SOFC Stick™ device 10. Thewires 42 are secured to the contact pads 44 by a solder connection 46,for example, to establish a reliable connection. Solders are a lowtemperature material, which can be used by virtue of being located inthe cold zones 30 of the SOFC Stick™ device 10. For example, a common10Sn88Pb2Ag solder can be used. The present invention eliminates theneed for high temperature voltage connections, thereby expanding thepossibilities to any low temperature connection material or means.

Also depicted in FIG. 3A, in perspective view, are the fuel outlet 16and the air outlet 22. The fuel enters through the fuel inlet 12 atfirst end 11 a, which is in one cold zone 30, and exits out the side ofSOFC Stick™ device 10 through outlet 16 adjacent the second end 11 b.Air enters through air inlet 18 located in the second end 11 b, which isin the cold zone 30, and exits from the air outlet 22 in the side of theSOFC Stick™ device 10 adjacent the first end 11 a. While the outlets 16and 22 are depicted as being on the same side of the SOFC Stick™ device10, it may be appreciated that they may be positioned at opposing sides,for example, as depicted below in FIG. 4A.

By having air outlet 22 close to fuel inlet 12 (and similarly fueloutlet 16 close to air inlet 18), and through the close proximity of theoverlapping layers (anode, cathode, electrolyte), the air outlet 22functions as a heat exchanger, usefully pre-heating the fuel that entersthe device 10 through fuel inlet 12 (and similarly, fuel outlet 16pre-heats air entering through air inlet 18). Heat exchangers improvethe efficiency of the system. The transition zones have overlappingareas of spent air and fresh fuel (and spent fuel and fresh air), suchthat heat is transferred before the fresh fuel (fresh air) reaches thehot zone. Thus, the SOFC Stick™ device 10 of the invention is amonolithic structure that includes a built-in heat exchanger.

With respect to FIG. 4A, there is depicted in perspective view theconnection of a plurality of SOFC Stick™ devices 10, in this case twoSOFC Stick™ devices, by aligning each contact pad 44 connected to theexposed anode portions 25 and soldering (at 46) a wire 42 connected tothe negative voltage node 38 to each of the contact pads 44. Similarly,the contact pads 44 that are connected to the exposed cathode portions27 are aligned and a wire 42 connecting the positive voltage node 40 issoldered (at 46) to each of those aligned contact pads 44, as shownpartially in phantom. As may be appreciated, because the connection isin the cold zone 30, and is a relatively simple connection, if one SOFCStick™ device 10 in a multi-SOFC Stick™ system or assembly needsreplacing, it is only necessary to break the solder connections to thatone device 10, replace the device with a new device 10, and re-solderthe wires 42 to the contact pads of the new SOFC Stick™ device 10.

FIG. 4B depicts in an end view the connection between multiple SOFCStick™ devices 10, where each SOFC Stick™ device 10 includes a pluralityof anodes and cathodes. For example, the specific embodiment depicted inFIG. 4B includes three sets of opposing anodes 24 and cathodes 26, witheach anode 24 exposed at the right side of the SOFC Stick™ device 10 andeach cathode exposed at the left side of the SOFC Stick™ device 10. Acontact pad is then placed on each side of the SOFC Stick™ device 10 tocontact the respective exposed anode portions 25 and exposed cathodeportions 27. On the right side, where the anodes 24 are exposed, thenegative voltage node 38 is connected to the exposed anode portions 25by securing wire 42 to the contact pad 44 via a solder connection 46.Similarly, positive voltage node 40 is connected electrically to theexposed cathode portions 27 on the left side of the SOFC Stick™ device10 by securing wire 42 to contact pad 44 via the solder connection 46.Thus, while FIGS. 1-4A depicted a single anode 24 opposing a singlecathode 26, it may be appreciated, as shown in FIG. 4B, that each SOFCStick™ device 10 may include multiple anodes 24 and cathodes 26, witheach being exposed to an outer surface of the SOFC Stick™ device 10 forelectrical connection by means of a contact pad 44 applied to the outersurface for connection to the respective voltage node 38 or 40. Thenumber of opposing anodes and cathodes in the structure may be tens,hundreds and even thousands.

FIG. 5 depicts in an end view a mechanical attachment for making theelectrical connection between wire 42 and the contact pad 44. In thisembodiment, the SOFC Stick™ devices 10 are oriented such that one set ofelectrodes is exposed at the top surface of each SOFC Stick™ device 10.The contact pad 44 has been applied to each top surface at one end(e.g., 11 a or 11 b) in the cold zone 30. Spring clips 48 may then beused to removably secure the wire 42 to the contact pads 44. Thus,metallurgical bonding may be used to make the electrical connections,such as depicted in FIGS. 3A, 4A and 4B, or mechanical connection meansmay be used, as depicted in FIG. 5. The flexibility in selecting anappropriate attachment means is enabled by virtue of the cold zones 30in the SOFC Stick™ devices of the invention. Use of spring clips orother mechanical attachment means further simplifies the process ofreplacing a single SOFC Stick™ device 10 in a multi-stick assembly.

FIGS. 6A and 6B depict in perspective views an alternative embodimenthaving a single cold zone 30 at the first end 11 a of SOFC Stick™ device10, with the second end 11 b being in the hot zone 32. In FIG. 6A, theSOFC Stick™ device 10 includes three fuel cells in parallel, whereas theSOFC Stick™ device 10 of FIG. 6B includes a single fuel cell. Thus,embodiments of the invention may include a single cell design or amulti-cell design. To enable the single end input of both the fuel andthe air, the air inlet 18 is reoriented to be adjacent the first end 11a at the side surface of the SOFC Stick™ device 10. The air passage 20(not shown) again runs parallel to the fuel passage 14, but in thisembodiment, the flow of air is in the same direction as the flow of fuelthrough the length of the SOFC Stick™ device 10. At the second end 11 bof the device 10, the air outlet 22 is positioned adjacent the fueloutlet 16. It may be appreciated that either the fuel outlet 16 or theair outlet 22, or both, can exit from a side surface of the SOFC Stick™device 10, rather than both exiting at the end surface.

As depicted in FIG. 6B, the supply tube 50 for the air supply 36 isformed by making holes through the side of the supply tube 50 andsliding the device 10 through the side holes so that the supply tube 50for the air supply 36 is perpendicular to the supply tube 50 for thefuel supply 34. Again, a silicone rubber tube or the like may be used inthis embodiment. A bonding material may be applied around the jointbetween the tube 50 and the device 10 to form a seal. The electricalconnections are also made adjacent the first end 11 a in the cold zone30. FIGS. 6A and 6B each depict the positive voltage connection beingmade on one side of the SOFC Stick™ device 10 and the negative voltageconnection being made on the opposing side of the SOFC Stick™ device 10.However, it may be appreciated that the invention is not so limited. Anadvantage of the single end input SOFC Stick™ device 10 is that there isonly one cold-to-hot transition instead of two transition zones 31, suchthat the SOFC Stick™ could be made shorter.

One benefit of the invention is the ability to make the active layersvery thin, thereby enabling an SOFC Stick™ to incorporate multiple fuelcells within a single device. The thinner the active layers are, thegreater the chance of an air passage 20 or fuel passage 14 caving induring manufacture of the SOFC Stick™ device 10, thereby obstructingflow through the passage. Therefore, in one embodiment of the invention,depicted in FIGS. 7A and 7B, a plurality of ceramic pillars 54 areprovided in the passages 14 and 20 to prevent distortion of theelectrolyte layer and obstruction of the passages. FIG. 7A is across-sectional side view, whereas FIG. 7B is a cross-sectional top viewthrough the air passage 20. According to one method of the invention,using the tape casting method, a sacrificial tape layer may be used,with a plurality of holes formed in the sacrificial layer, such as bymeans of laser removal of the material. A ceramic material is then usedto fill the holes, such as by spreading a ceramic slurry over thesacrificial tape layer to penetrate the holes. After the various layersare assembled together, the sacrificial material of the sacrificiallayer is removed, such as by use of a solvent, leaving the ceramicpillars 54 remaining.

In another embodiment for forming the ceramic pillars 54, largeparticles of a pre-sintered ceramic can be added to an organic vehicle,such as plastic dissolved in a solvent, and stirred to form a randommixture. By way of example and not limitation, the large particles maybe spheres, such as 0.002 in. diameter balls. The random mixture is thenapplied to the green structure, such as by printing in the areas wherethe fuel and air passages 14 and 20 are to be located. During thesintering (bake/fire) process, the organic vehicle leaves the structure(e.g. is burned out), thereby forming the passages, and the ceramicparticles remain to form the pillars 54 that physically hold open thepassages. The resultant structure is shown in the micrographs of FIGS.7C and 7D. The pillars 54 are randomly positioned, with the averagedistance being a function of the loading of the ceramic particles in theorganic vehicle.

FIG. 8A depicts in cross-section one embodiment of the inventioncontaining two fuel cells in parallel. Each active electrolyte layer 28has an air passage 20 and cathode layer 26 a or 26 b on one side and afuel passage 14 and anode layer 24 a or 24 b on the opposing side. Theair passage 20 of one fuel cell is separated from the fuel passage 14 ofthe second fuel cell by ceramic material 29. The exposed anode portions25 are each connected via wire 42 to the negative voltage node 38 andthe exposed cathode portions 27 are each connected via a wire 42 to thepositive voltage node 40. A single air supply 36 can then be used tosupply each of the multiple air passages 20 and a single fuel supply 34may be used to supply each of the multiple fuel passages 14. Theelectrical circuit established by this arrangement of the active layersis depicted at the right side of the figure.

In the cross-sectional view of FIG. 8B, the SOFC Stick™ device 10 issimilar to that depicted in FIG. 8A, but instead of having multipleexposed anode portions 25 and multiple exposed cathode portions 27, onlyanode layer 24 a is exposed at 25 and only one cathode layer 26 a isexposed at 27. A first via 56 connects cathode layer 26 a to cathodelayer 26 b and a second via 58 connects anode layer 24 a to anode layer24 b. By way of example, laser methods may be used during formation ofthe green layers to create open vias, which are then subsequently filledwith electrically conductive material to form the via connections. Asshown by the circuit at the right of FIG. 8B, the same electrical pathis formed in the SOFC Stick™ device 10 of FIG. 8B as in the SOFC Stick™device 10 of FIG. 8A.

FIGS. 9A and 9B also depict, in cross-section views, multi-fuel celldesigns, but with shared anodes and cathodes. In the embodiment of FIG.9A, the SOFC Stick™ device 10 includes two fuel passages 14 and two airpassages 20, but rather than having two fuel cells, this structureincludes three fuel cells. The first fuel cell is formed between anodelayer 24 a and cathode layer 26 a with intermediate electrolyte layer28. Anode layer 24 a is on one side of a fuel passage 14, and on theopposing side of that fuel passage 14 is a second anode layer 24 b.Second anode layer 24 b opposes a second cathode layer 26 b with anotherelectrolyte layer there between, thereby forming a second fuel cell. Thesecond cathode layer 26 b is on one side of an air passage 20 and athird cathode layer 26 c is on the opposing side of that air passage 20.Third cathode layer 26 c opposes a third anode layer 24 c with anelectrolyte layer 28 therebetween, thus providing the third fuel cell.The portion of the device 10 from anode layer 24 a to cathode layer 26 ccould be repeated numerous times within the device to provide the sharedanodes and cathodes thereby multiplying the number of fuel cells withina single SOFC Stick™. Each anode layer 24 a, 24 b, 24 c includes anexposed anode portion 25 to which electrical connections can be made atthe outer surface of the SOFC Stick™ device 10 to connect to a negativevoltage node 38 via a wire 42, for example. Similarly, each cathodelayer 26 a, 26 b, 26 c includes an exposed cathode portion 27 to theoutside surface for connection to a positive voltage node 40 via a wire42, for example. A single air supply 36 may be provided at one cold endto supply each of the air passages 20 and a single fuel supply 34 may beprovided at the opposite cold end to supply each of the fuel passages14. The electrical circuit formed by this structure is provided at theright side of FIG. 9A. This SOFC Stick™ device 10 contains three fuelcell layers in parallel trebling the available power. For example, ifeach layer produces 1 volt and 1 amp, then each fuel cell layer produces1 watt of power output (volt×amp=watt). Therefore, this three-layerlayout would then produce 1 volt and 3 amps for a total of 3 watts ofpower output.

In FIG. 9B, the structure of FIG. 9A is modified to provide a singleelectrical connection to each of the voltage nodes to create three fuelcells in series, as shown by the circuit at the right side of FIG. 9B.The positive voltage node 40 is connected to cathode layer 26 a atexposed cathode portion 27. Anode layer 24 a is connected to cathodelayer 26 b by via 58. Anode layer 24 b is connected to cathode layer 26c by via 56. Anode layer 24 c is then connected at exposed anode portion25 to the negative voltage node 38. Thus, using the same 1 amp/1 voltper layer assumption, this three cell structure would produce 3 voltsand 1 amp for a total of 3 watts of power output.

Another embodiment of the invention is depicted in side view in FIG. 10.In this embodiment, the SOFC Stick™ device 10 has a single cold zone 30at the first end 11 a with the second end 11 b being in the hot zone 32.As in other embodiments, the fuel inlets 12 are at the first end 11 aand connected to a fuel supply 34 by a supply tube 50. In thisembodiment, the fuel passages 14 extend the length of the SOFC Stick™device 10 with the fuel outlet 16 being at second end 11 b. Thus, thefuel supply connection is made in the cold zone 30 and the outlet forthe fuel reactants (e.g., CO₂ and H₂O) is in the hot zone 32. Similarly,the anodes have an exposed anode portion 25 in the cold zone 30 forconnecting to the negative voltage node 38 via a wire 42.

In the embodiment of FIG. 10, the SOFC Stick™ device 10 is open at leastone side, and potentially at both opposing sides, to provide both airinlets 18 and air passages 20 in the hot zone 32. The use of supportingceramic pillars 54 may be particularly useful in this embodiment withinthe air passages 20. The air outlet can be at the second end 11 b, asdepicted. Alternatively, although not shown, the air outlet may be at anopposing side from the air inlet side if the passages 20 extend throughthe width and the air supply is directed only toward the input side, orif the passages 20 do not extend through the width. Instead of providingonly heat to the hot zone 32, in this embodiment, air is also provided.In other words, the sides of the device 10 in the hot zone 32 are opento heated air instead of supplying air through a forced air tube.

FIG. 10A shows in side view a variation of the embodiment depicted inFIG. 10. In FIG. 10A, the SOFC Stick™ device 10 includes opposing coldzones 30 with a central heated zone 32 separated from the cold zones 30by transition zones 31. The air inlet 18 is provided in the centralheated zone 32, in at least a portion thereof, to receive the heatedair. However, in this embodiment, the air passage is not completely opento the side of the SOFC Stick™ device 10 for an appreciable length as inFIG. 10. Rather, as shown more clearly in FIG. 10B, air passage 20 isopen in a portion of the hot zone 32 and then is close to the sides forthe remainder of the length and then exits at air outlet 22 at secondend 11 b of the SOFC Stick™ device 10. This embodiment allows heated airto be supplied in the hot zone 32 rather than a forced air supply tube,but also allows for the fuel and air to exit at one end 11 b of thedevice 10 in a cold zone 30.

While specific embodiments have been depicted and described in detail,the scope of the invention should not be so limited. More generalembodiments of the invention are described below and may be understoodmore fully with reference to the schematic views depicted in FIGS.11-24. FIG. 11 provides a key for the components depicted schematicallyin FIGS. 12-24. Where fuel (F) or air (A) is shown by an arrow goinginto the SOFC Stick™ device, that indicates forced flow, such as througha tube connected to the input access point. Where air input is notdepicted, that indicates that heated air is supplied in the hot zone bymeans other than a forced flow connection and the SOFC Stick™ is open tothe air passage at an access point within the hot zone.

One embodiment of the invention is an SOFC Stick™ device that includesat least one fuel passage and associated anode, at least one oxidantpathway and associated cathode, and an electrolyte therebetween, wherethe cell is substantially longer than it is wide or thick so as to havea CTE in one dominant axis and operating with a portion thereof in aheated zone having a temperature of greater than about 400° C. In thisembodiment, the SOFC Stick™ device has integrated access points for bothair and fuel input at one end of the device according to the dominantCTE direction, or air input at one end and fuel input at the other endaccording to the dominant CTE direction, and air and fuel inputs beinglocated outside the heated zone. For example, see FIGS. 20 and 24.

In another embodiment of the invention, the fuel cell has a firsttemperature zone and a second temperature zone, wherein the firsttemperature zone is the hot zone, which operates at a temperaturesufficient to carry out the fuel cell reaction, and the secondtemperature zone is outside the heated zone and operates at a lowertemperature than the first temperature zone. The temperature of thesecond temperature zone is sufficiently low to allow low temperatureconnections to be made to the electrodes and a low temperatureconnection for at least the fuel supply. The fuel cell structure extendspartially into the first temperature zone and partially into the secondtemperature zone. For example, see FIGS. 12, 13 and 17.

In one embodiment of the invention, the fuel cell includes a firsttemperature zone that is the heated zone and a second temperature zoneoperating at a temperature below 300° C. The air and fuel connectionsare made in the second temperature zone using rubber tubing or the likeas a low temperature connection. Low temperature solder connections orspring clips are used to make the electrical connections to the anodeand cathode for connecting them to the respective negative and positivevoltage nodes. Further, the fuel outlet for carbon dioxide and water andthe air outlet for depleted oxygen are located in the first temperaturezone, i.e., the heated zone. For example, see FIG. 17.

In another embodiment, the fuel cell structure has a central firsttemperature zone that is the heated zone, and each end of the fuel cellis located outside the first temperature zone in a second temperaturezone operating below 300° C. Fuel and air inputs are located in thesecond temperature zone, as are solder connections or spring clips forelectrical connection to the anode and cathode. Finally, output for thecarbon dioxide, water and depleted oxygen are located in the secondtemperature zone. For example, see FIGS. 19, 20 and 24.

In another embodiment of the invention, fuel inputs may be provided ateach end according to the dominant CTE direction in a second temperaturezone operating below 300° C. with a first temperature zone being theheated zone provided in the center between the opposing secondtemperature zones. The output for the carbon dioxide, water, anddepleted oxygen may be located in the central heated zone. For example,see FIGS. 15 and 18. Alternatively, the output for the carbon dioxide,water and depleted oxygen may be located in the second temperature zone,i.e., outside of the heated zone. For example, see FIGS. 16 and 19.

In another embodiment, both the fuel and air input access points arelocated outside the first temperature zone, which is the heated zone, ina second temperature zone operating below 300° C. thereby allowing useof low temperature connections, such as rubber tubing for air and fuelsupply. In addition, solder connections or spring clips are used in thesecond temperature zone for connecting the voltage nodes to anodes andcathodes. In one embodiment, the fuel and air input are both at one endaccording to the dominate CTE direction, with the other end of the SOFCStick™ being in the first heated temperature zone with the outputs ofcarbon dioxide, water and depleted oxygen being in the heated zone. Forexample, see FIG. 17. Thus, the SOFC Stick™ has one heated end and onenon-heated end.

In another embodiment, fuel and air are inputted into one end accordingto the dominant CTE direction outside the heated zone and exit at theopposite end also outside the heated zone, such that the heated zone isbetween two opposing second temperature zones. For example, see FIG. 20.In yet another alternative, fuel and air are inputted into both ofopposing ends located in second temperature zones with the fuel and airoutputs being in the central heated zone. For example, see FIG. 18.

In yet another alternative, fuel and air are inputted into both ofopposing ends located in second temperature zones with the respectiveoutputs being in the second temperature zone at the opposite end fromthe input. For example, see FIG. 19. Thus, the fuel cell has a centralheated zone and opposing ends outside the heated zone, with fuel and airboth inputted into the first end with the respective reaction outputsexiting adjacent the second end, and both fuel and air being inputtedinto the second end and the reaction outputs exiting adjacent the firstend.

In yet another embodiment, fuel input may be at one end outside theheated zone and air input may be at the opposite end outside the heatzone. For example, see FIGS. 21-24. In this embodiment, the reactionoutputs from both the air and fuel may be within the heated zone (seeFIG. 21), or they both may be outside the heated zone adjacent theopposite end from the respective input (see FIG. 24). Alternatively, thecarbon dioxide and water output may be in the hot zone while thedepleted oxygen output is outside the hot zone (see FIG. 22), orconversely, the depleted oxygen output may be in the heated zone and thecarbon dioxide and water output outside the heated zone (see FIG. 23).The variations with respect to fuel and air output depicted in FIGS. 22and 23 could also be applied in the embodiments depicted in FIGS. 18-20,for example.

In another embodiment of the invention, depicted in top plan view inFIGS. 25A and 27A and in side view in FIG. 27B, an SOFC Stick™ device100 is provided having what may be referred to as a panhandle design.The SOFC Stick™ device 100 has an elongate section 102, which may besimilar in dimension to the Stick™ devices depicted in priorembodiments, that has a CTE in one dominant axis, i.e., it issubstantially longer than it is wide or thick. The SOFC Stick™ device100 further has a large surface area section 104 having a width thatmore closely matches the length. Section 104 may have a square surfacearea or a rectangular surface area, but the width is not substantiallyless than the length, such that the CTE does not have a single dominantaxis in section 104, but rather has a CTE axis in the length directionand the width direction. The large surface area section 104 is locatedin the hot zone 32, whereas the elongate section 102 is at leastpartially located in the cold zone 30 and the transition zone 31. In anexemplary embodiment, a portion of the elongate section 102 extends intothe hot zone 32, but this is not essential. By way of example, the fueland air supplies may be connected to the elongate section 102 in themanner depicted in FIG. 6B, as well as the electrical connections.

In FIGS. 25B and 26A, a top plan view is provided and in FIG. 26B a sideview is provided of an alternative embodiment similar to that shown inFIGS. 25A, 27A and 27B but further having a second elongate section 106opposite the elongate section 102 so as to position the large surfacearea section 104 between the two elongate sections 102 and 106. Elongatesection 106 is also at least partially located in a cold zone 30 and atransition zone 31. In this embodiment, fuel may be inputted intoelongate section 102 and air inputted into elongate section 106. By wayof example, the air supply and the fuel supply could then be connectedto the elongate sections 106 and 102, respectively, in the mannerdepicted in FIG. 2 or FIG. 3B. As depicted in FIG. 25B, the air outputmay be located in the elongate section 102 adjacent the fuel input, andthe fuel output may be located in elongate section 106 adjacent the airinput. Alternatively, one or both of the air and fuel outputs may belocated in the large surface area section 104 in the hot zone 32, asdepicted in FIGS. 26A and 26B in top and side views, respectively. Itmay be appreciated that in the embodiments of FIGS. 25A and 25B, thesurface area of the opposing anode and cathode with interveningelectrolyte may be increased in the hot zone to increase the reactionarea, thereby increasing the power generated by the SOFC Stick™ device100.

Another benefit of the SOFC Stick™ devices 10, 100 of the invention islow weight. Typical combustion engines weigh on the order of 18-30 lbsper kW of power. An SOFC Stick™ device 10, 100 of the invention can bemade with a weight on the order of 0.5 lbs per kW of power.

FIGS. 28A-D depict an alternative embodiment of a Tubular SOFC Stick™device 200 of the invention, having a spiral or rolled, tubularconfiguration. FIG. 28A is a schematic top view of device 200, in theunrolled position. The unrolled structure of device 200 has a first end202 and a second end 204 of equal length L that will correspond to thelength of the rolled or spiral Tubular SOFC Stick™ device 200. Fuelinlet 12 and air inlet 18 are shown on opposing sides adjacent first end202. Fuel passage 14 and air passage 20 then extend along the width ofthe unrolled structure of device 200 to the second end 204 such that thefuel outlet 16 and air outlet 22 are at the second end 204, as furthershown in the schematic end view of the unrolled structure of device 200in FIG. 28B and the schematic side view of the unrolled structure ofdevice 200 in FIG. 28C. The fuel passage 14 and air passage 20 are shownas extending nearly the length L of the unrolled structure of device 200so as to maximize fuel and air flow, but the invention is not solimited. To form the spiral Tubular SOFC Stick™ device 200, first end202 is then rolled toward second end 204 to form the spiral tubestructure of device 200 depicted in the schematic perspective view ofFIG. 28D. Air supply 36 may then be positioned at one end of the spiralTubular SOFC Stick™ device 200 for input into air inlet 18, while thefuel supply 34 may be positioned at the opposite end of the spiralTubular SOFC Stick™ device 200 to input fuel into the fuel inlet 12. Theair and the fuel will then exit the spiral Tubular SOFC Stick™ device200 along the length L of the device 200 through fuel outlet 16 and airoutlet 22. The voltage nodes 38, 40 can be soldered to contact pads 44formed on or adjacent to opposing ends of the spiral Tubular SOFC Stick™device 200.

FIGS. 29A-29G depict an alternative embodiment of the invention whereinthe SOFC Stick™ device is in a tubular concentric form. FIG. 29A depictsin schematic isometric view a concentric Tubular SOFC Stick™ device 300.FIGS. 29B-29E depict cross-sectional views of the concentric device 300of FIG. 29A. FIG. 29F depicts an end view at the air input end of thedevice 300, and FIG. 29G depicts an end view at the fuel input end ofdevice 300. The particular embodiment shown includes three air passages20, one being in the center of the tubular structure and the other twobeing spaced from and concentric therewith. The concentric Tubular SOFCStick™ device 300 also has two fuel passages 14 between and concentricwith the air passages 20. As shown in FIGS. 29A-29D, the concentricTubular SOFC Stick™ device 300 includes a fuel outlet 16 connecting thefuel passages 14 at one end and an air outlet 22 connecting the airpassages 20 at the other end opposite their respective inlets. Each airpassage 20 is lined with cathodes 26 and each fuel passage 14 is linedwith anodes 24, with electrolyte 28 separating opposing anodes andcathodes. As shown in FIGS. 29A-29B and 29F-29G, electrical connectionmay be made to the exposed anodes 25 and exposed cathodes 27 at opposingends of the concentric Tubular SOFC Stick™ device 300. Contact pads 44may be applied to the ends to connect the exposed anodes 25 and exposedcathodes 27, and although not shown, the contact pads 44 can be runalong the outside of the device 300 to permit the electrical connectionto be made at a point along the length of the device 300 rather than atthe ends. Concentric Tubular SOFC Stick™ device 300 may include pillars54 positioned within the air and fuel passages 14, 20 for structuralsupport.

In the embodiments of the invention having two cold zones 30 at opposingends 11 a, 11 b, with air input and fuel output at one end and fuelinput and air output at the opposing end, the spent fuel or air is in aheated state as it exits the central hot zone 32. The heated air andfuel cool as they travel through the transition zones 31 to the coldzones 30. Thin layers of electrodes and/or ceramic/electrolyte separatean air passage from a parallel fuel passage, and vice-versa. In onepassage, heated air is exiting the hot zone, and in an adjacent parallelpassage, fuel is entering the hot zone, and vice-versa. The heated air,through heat exchange principles, will heat up the incoming fuel in theadjacent parallel passage, and vice-versa. Thus, there is somepre-heating of the air and fuel through heat exchange. However, due tothe rapid loss of heat outside the hot zone, as discussed above, heatexchange may not be sufficient to pre-heat the air and fuel to theoptimal reaction temperature before it enters the active region in thehot zone. In addition, in embodiments where the SOFC Stick™ device 10includes one cold end and one hot end, fuel and air are inputted intothe same cold end and exit through the same opposing hot end, such thatthere is no cross-flow of fuel and air for heat-exchange to occur. Onlylimited heat exchange to the incoming fuel and air is available from theelectrode and ceramic materials of the SOFC Stick™ device.

FIGS. 30A-33C depict various embodiments of an SOFC Stick™ device 10having integrated pre-heat zones 33 a for heating the fuel and airbefore it enters an active zone 33 b in which the anodes 24 and cathodes26 are in opposing relation. These embodiments include SOFC Stick™devices in which there are two cold ends with an intermediate hot zoneand fuel and air input at opposing cold ends, and SOFC Stick™ devices inwhich there is one hot end and one cold end with fuel and air input bothat the single cold end. In these embodiments, the amount of electrodematerial used can be limited to the active zone 33 b with only a smallamount leading to the cold zone for the external connection to thevoltage nodes 38, 40. Another benefit in these embodiments, which willbe described in more detail later, is that the electrons have theshortest possible path to travel to the external voltage connection,which provides a low resistance.

FIG. 30A depicts a schematic cross-sectional side view of a firstembodiment of an SOFC Stick™ device 10 having one cold zone 30 and oneopposing hot zone 32 with an integrated pre-heat zone 33 a. FIG. 30Bdepicts in cross-section a view through the anode 24 looking up towardthe fuel passage 14, and FIG. 30C depicts in cross-section a viewthrough the cathode 26 looking down toward the air passage 20. As shownin FIGS. 30A and 30B, the fuel from fuel supply 34 enters through fuelinlet 12 and extends along the length of the device 10 through fuelpassage 14 and exits from the opposite end of the device 10 through fueloutlet 16. The cold zone 30 is at the first end 11 a of SOFC Stick™device 10 and the hot zone 32 is at the opposing second end 11 b.Between the hot and cold zones is the transition zone 31. The hot zone32 includes an initial pre-heat zone 33 a through which the fuel firsttravels, and an active zone 33 b that includes the anode 24 adjacent thefuel passage 14. As shown in FIG. 30B, the cross-sectional area of theanode 24 is large in the active zone 33 b. The anode 24 extends to oneedge of the SOFC Stick™ device 10 and an exterior contact pad 44 extendsalong the outside of the device 10 to the cold zone 30 for connection tothe negative voltage node 38.

Similarly, as shown in FIGS. 30A and 30C, the air from air supply 36enters through the air inlet 18 positioned in the cold zone 30 and theair extends along the length of the SOFC Stick™ device 10 through airpassage 20 and exits from the hot zone 32 through the air outlet 22.Because the air and fuel are entering at the same end and travelingalong the length of the SOFC Stick™ device 10 in the same direction,there is limited pre-heating of the air and fuel by heat exchange priorto the hot zone 32. The cathode 26 is positioned in the active zone 33 bin opposing relation to the anode 24 and extends to the opposite side ofthe SOFC Stick™ device 10 where it is exposed and connected to anexternal contact pad 44 that extends from the active hot zone 33 b tothe cold zone 30 for connection to the positive voltage node 40. It isnot necessary, however, that the exposed cathode 27 be on an oppositeside of the device 10 as the exposed anode 25. The exposed anode 25 andexposed cathode 27 could be on the same side of the device and thecontact pads 44 could be formed as stripes down the side of the SOFCStick™ device 10. By this structure, the air and fuel are first heatedin the pre-heat zone 33 a, where no reaction is taking place, and themajority of the anode and cathode material is limited to the active zone33 b where the heated air and fuel enter and react by virtue of theopposed anode and cathode layers 24, 26.

The embodiment depicted in FIGS. 31A-31C is similar to that depicted inFIGS. 30A-30C, but rather than having one hot end and one cold end, theembodiment of FIGS. 31A-C includes opposing cold zones 30 with a centralhot zone 32. Fuel from fuel supply 34 enters through the first end 11 aof device 10 through fuel inlet 12 in the cold zone 30 and exits fromthe opposite second end 11 b through fuel outlet 16 positioned in theopposing cold zone 30. Similarly, air from air supply 36 enters throughthe opposite cold zone 30 through air inlet 18 and exits at the firstcold zone 30 through air outlet 22. The fuel enters the hot zone 32 andis pre-heated in pre-heat zone 33 a, while the air enters at theopposite side of the hot zone 32 and is pre-heated in another pre-heatzone 33 a. There is thus a cross-flow of fuel and air. The anode 24opposes the cathode 26 in an active zone 33 b of hot zone 32 and thereaction occurs in the active zone 33 b involving the pre-heated fueland air. Again, the majority of electrode material is limited to theactive zone 33 b. The anode is exposed at one edge of the SOFC Stick™device 10, and the cathode is exposed at the other side of device 10. Anexternal contact pad 44 contacts the exposed anode 25 in the hot zone 32and extends toward the first cold end 11 a for connection to negativevoltage node 38. Similarly, an external contact pad 44 contacts theexposed cathode 27 in hot zone 32 and extends toward the second coldzone 11 b for connection to positive voltage node 40.

The pre-heat zones 33 a provide the advantage of fully heating the gasto the optimal reaction temperature before it reaches the active region.If the fuel is colder than the optimum temperature, the efficiency ofthe SOFC system will be lower. As the air and fuel continue on theirpaths, they warm up. As they warm up, the efficiency of the electrolyteincreases in that region. When the fuel, air and electrolyte reach thefull temperature of the furnace, then the electrolyte is working underits optimal efficiency. To save money on the anode and cathode, whichmay be made out of precious metal, the metal can be eliminated in thoseareas that are still below the optimal temperature. The amount of thepre-heat zone, in terms of length or other dimensions, depends on theamount of heat transfer from the furnace to the SOFC Stick™ device, andfrom the SOFC Stick™ device to the fuel and air, as well as whether anyheat exchange is occurring due to cross-flow of the fuel and air. Thedimensions further depend on the rate of flow of fuel and air; if thefuel or air is moving quickly down the length of the SOFC Stick™ device,a longer pre-heat zone will be advantageous, whereas if the flow rate isslow, the pre-heat zone may be shorter.

FIGS. 32A and 32B depict an embodiment similar to that shown in FIGS.31A-31C, but the SOFC Stick™ device 10 includes a pre-heat chamber 13between the fuel inlet 12 and fuel passage 14 that extends into the hotzone 32 for pre-heating in the pre-heat zone 33 a a large volume of fuelbefore it passes through the more narrow fuel passage 14 into the activezone 33 b. The SOFC Stick™ device 10 similarly includes a pre-heatchamber 19 between the air inlet 18 and the air passage 20 that extendsinto the hot zone 32 for pre-heating a large volume of air in thepre-heat zone 33 a before it passes through the more narrow air passage20 to the active zone 33 b. As disclosed in embodiments above, the SOFCStick™ device 10 may include multiple fuel passages 14 and air passages20, each of which would receive flow from a respective pre-heat chamber13, 19.

With respect to a high-volume pre-heat chamber instead of a pre-heatchannel, it may be imagined, by way of example only, that if it takes 5seconds for a molecule of air to heat up to the optimal temperature,then if the molecules of air are traveling down the SOFC Stick™ device10 at 1 inch per second, the SOFC Stick™ device would need a pre-heatchannel that is 5 inches in length before the air enters the active zone33 b. If, however, a large volume chamber is provided instead of achannel, the volume permits the molecules to spend additional time inthe cavity before entering the more narrow channel to the active zone,such that the air molecules are heated in the chamber and then a shortlength of channel may be used for feeding the heated air molecules tothe active zone. Such a cavity or pre-heat chamber could be prepared ina number of different ways, including taking a green (i.e., beforesintering) assembly and drilling into the end of the assembly to formthe chamber, or by incorporating a large mass of organic material withinthe green stack as it is formed, whereby the organic material is bakedout of the SOFC Stick™ device during sintering.

FIGS. 33A-33C depict yet another embodiment for pre-heating the air andfuel prior to the air and fuel reaching the active zone 33 b. FIG. 33Ais a schematic cross-sectional side view, essentially through thelongitudinal center of the SOFC Stick™ device 10. FIG. 33B is across-sectional top view taken along the line 33B-33B where the fuelpassage 14 and anode 24 intersect, while FIG. 33C is a cross-sectionalbottom view taken along the line 33C-33C where the air passage 20intersects the cathode 26. The SOFC Stick™ device 10 has two opposingcold zones 30 and a central hot zone 32, with a transition zone 31between each cold zone 30 and the hot zone 32. Fuel from fuel supply 34enters the first end 11 a of SOFC Stick™ device 10 through fuel inlet 12and travels through the fuel passage 14, which extends toward theopposite end of the hot zone 32, where it makes a U-turn and travelsback to the cold zone 30 of first end 11 a, where the spent fuel exitsthrough fuel outlet 16. Similarly, air from air supply 36 enters thesecond end 11 b of SOFC Stick™ device 10 through the air inlet 18 andtravels through the air passage 20, which extends toward the opposingend of the hot zone 32, where it makes a U-turn and travels back to thesecond end 11 b, where the air exits from the cold zone 30 through airoutlet 22. By means of these U-turned passages, the portion of the fuelpassage 14 and air passage 20 from the initial entry into the hot zone32 through the bend (U-turn) constitute a pre-heat zone for heating thefuel and air. After the bends, or U-turns, in the passages 14, 20, thepassages are lined with a respective anode 24 or cathode 26, which arein opposing relation with an electrolyte 28 therebetween, which regionconstitutes the active zone 33 b in hot zone 32. Thus, the fuel and airis heated in the pre-heat zone 33 a prior to entry into the active zone33 b to increase the efficiency of the SOFC Stick™ device 10, and tominimize the usage of electrode material. The anode 24 is extended tothe exterior of the device 10 in the cold zone 30 for connection tonegative voltage node 38. Similarly, cathode 26 is extended to theexterior of the device 10 for electrical connection to positive voltagenode 40. The fuel and air outlets 16 and 22 also may exit from the coldzones 30.

In many of the embodiments shown and described above, the anodes 24 andcathodes 26 travel within the layers of the SOFC Stick™ device 10,essentially in the center area of each layer, i.e., internal to thedevice, until they reach the end of the device. At that point, theanodes 24 and cathodes 26 are tabbed to the outside of the SOFC Stick™device 10 where the exposed anode 25 and exposed cathode 27 aremetallized with a contact pad, such as by applying a silver paste, andthen a wire is soldered to the contact pad. For example, see FIGS.4A-4B. It may be desirable, however, to build up the layers in the SOFCStick™ device 10 into higher voltage combinations, for example as shownin FIGS. 8A-9B. If it is desired to make an SOFC Stick™ device thatproduces 1 kW of power, the power is divided between the voltage and thecurrent. One standard is to use 12 volts, such that 83 amps would beneeded to create the total 1 kW of power. In FIGS. 8B and 9B, vias wereused to interconnect the electrode layers to form parallel or seriescombinations.

Alternative embodiments for interconnecting the electrode layers aredepicted in FIGS. 34A to 37. Rather than interconnecting the electrodelayers in the interior of the SOFC Stick™ device 10, these alternativeembodiments use exterior stripes (narrow contact pads), for example ofsilver paste, along the sides of the SOFC Stick™ device 10, inparticular, multiple small stripes. Using the striping technique, asimple structure is formed that can provide series and/or parallelcombinations to achieve any current/voltage ratios needed. Moreover, theexternal stripes will have loose mechanical tolerances compared to theinternal vias, thereby simplifying manufacturing. Also, the externalstripes will likely have a lower resistance (or equivalent seriesresistance) than the vias. Lower resistance in a conductor path willresult in lower power loss along that path, such that the externalstripes provide the ability to remove the power from the SOFC Stick™device 10 with a lower loss of power.

Referring now specifically to FIGS. 34A and 34B, an externalanode/cathode interconnect in series is depicted. FIG. 34A provides aschematic oblique front view of the alternating anodes 24 a, 24 b, 24 cand cathodes 26 a, 26 b, 26 c. Along the length of the SOFC Stick™device 10, the anodes 24 a, 24 b, 24 c and cathodes 26 a, 26 b, 26 cinclude a tab out to the edge of the device 10 to provide the exposedanodes 25 and exposed cathodes 27. An external contact pad 44 (orstripe) is then provided on the outside of the SOFC Stick™ device overthe exposed anodes 25 and cathodes 27, as best shown in the schematicside view of FIG. 34B. By connecting the three pairs of opposed anodes24 a, 24 b, 24 c and cathodes 26 a, 26 b, 26 c in series, the SOFCStick™ device 10 provides 3 volts and 1 amp. In FIG. 35, the structureis doubled and the two structures are connected by long stripes down thesides of the device 10, thereby providing an external anode/cathodeinterconnect in a series parallel design that provides 3 volts and 2amps.

FIGS. 36A and 36B provide an embodiment for a low equivalent seriesresistance path for providing low power loss. In this embodiment, thehot zone 32 is in the center of the SOFC Stick™ device 10 with the firstend 11 a and second end 11 b being in cold zones 30. Fuel is inputtedthrough fuel inlets 12 in first end 11 a and air is inputted through airinlets 18 in second end 11 b. Within the hot zone 32, which is theactive area of the SOFC Stick™ device 10, the anodes 24 and cathodes 26are exposed to the sides of the device, with the anodes 24 exposed toone side, and the cathodes 26 exposed to the opposite side. Contact pads44 (or stripes) are applied over the exposed anodes 25 and cathodes 27.Then, the edges of the SOFC Stick™ device 10 are metallized along thelength of the sides of the device 10 until the metallization reaches thecold zones 30, where the low temperature solder connection 46 is made tothe negative voltage node 38 and the positive voltage node 40. Theanodes 24 and cathodes 26 cannot be optimized only for low resistancebecause they have other functions. For example, the electrodes must beporous to allow the air or fuel to pass through to the electrolyte, andporosity increases resistance. Further, the electrodes must be thin toallow for good layer density in a multi-layer SOFC Stick™ device 10, andthe thinner the electrode, the higher the resistance. By adding thickercontact pads 44 to the edges (sides) of the SOFC Stick™ device, it ispossible to provide a low resistance path toward the solder connection46. The thicker the contact pad 44, the lower the resistance. If anelectron must travel 10 inches, for example, down the electrode withinthe SOFC Stick™ device 10, past all the voids in the electrode layer,the path of least resistance would be to travel 0.5 inch, for example,to the side edge of the device 10, and then travel the 10 inches downthe exterior non-porous contact pad 44. Thus, the long contact pads 44along the exterior of the SOFC Stick™ device that extend to the coldzones 30 allow for the power to be removed from the SOFC Stick™ device10 with a lower loss by providing a lower resistance conductor path.Thus, the striping technique may be used in the active area (hot zone32) of the SOFC Stick™ device 10 for making series and parallelconnections to increase power, and a long stripe down the side of thedevice to the cold ends allows that power to be efficiently removed fromthe SOFC Stick™ device 10.

FIG. 37 depicts, in schematic isometric view, an embodiment similar tothat depicted in FIG. 36B, but having a single cold zone 30 at the firstend 11 a of the SOFC Stick™ device 10, with the hot zone 32 being at thesecond end 11 b of device 10. Multiple vertical stripes or contact pads44 are provided within the hot zone 32 to make the series and/orparallel connections, and the horizontal long stripes 44 down the sidesof the device 10 are provided from the hot zone 32 to the cold zone 30for making the low temperature solder connections 46 to the positivevoltage node 40 and negative voltage node 38.

One method for forming the fuel passages 14 and air passages 20 is toplace an organic material within the green, layered structure that canthen bake out during a later sintering step. To build individual SOFCSticks™ having high power output, such as 1 kW or 10 kW output, the SOFCStick™ must be long, wide and have a high layer count. By way ofexample, the SOFC Stick™ devices may be on the order of 12 inches to 18inches long. When baking the green structure to sinter the ceramic andremove the organic material, the organic material used to form the fuelpassage 14 must exit through openings 12 and 16 that form the fuel inletand fuel outlet, respectively. Similarly, the organic material used toform the air passage 20 must bake out through the openings 18 and 22that form the air inlet and air outlet, respectively. The longer andwider the devices, the more difficult it is for the organic material toexit through these openings. If the device is heated too fast duringbake-out, the various layers can delaminate because the decomposition ofthe organic material occurs faster than the material can exit thestructure.

FIGS. 38A and 38B depict, in schematic cross-sectional side view, analternative embodiment that provides multiple exit gaps for bake-out ofthe organic material 72. As shown in FIG. 38A, multiple openings 70 areprovided on one side of the SOFC Stick™ device 10 to provide multiplebake-out paths for the organic material 72 to exit the structure. Asdepicted in FIG. 38B, after bake-out, the multiple openings 70 are thenclosed by applying a barrier coating 60 to the side of the SOFC Stick™device 10. By way of example, the barrier coating may be a glasscoating. In another example, the barrier coating may be a glasscontaining a ceramic filler. In yet another embodiment, the barriercoating 60 may be a contact pad 44, for example filled with paste, whichwould then also serve as the low resistance path for the generatedpower. The silver paste may also contain glass for increased adhesion.In an exemplary embodiment, the bake-out paths for the cathode arevented to one side of the SOFC Stick™ device 10 and the bake-out pathsfor the anode are vented to the opposing side of the device 10 to avoidshorting between opposite electrodes.

In an alternative embodiment for an SOFC Stick™ device 10, 100, 200,300, rather than having an open air passage 20 and fuel passage 14 linedwith a cathode 26 or anode 24, respectively, the cathode and air channelmay be combined and the anode and fuel channel may be combined throughuse of porous electrode materials that permit flow of the air or fuel.The cathodes and anodes must be porous anyway to permit the reaction tooccur, so in combination with forced air and fuel input, sufficient flowcould be achieved through the SOFC Stick™ device to permit the powergenerating reaction to occur.

Another embodiment of the present invention is depicted in schematiccross-sectional end view in FIG. 39. This embodiment is essentially ananode-supported version of an SOFC Stick™ device 10. As with otherembodiments, the SOFC Stick™ device 10 may have a hot end and a cold endor two cold ends with an intermediate hot zone. Rather than having thedevice 10 supported by ceramic 29, the anode-supported version uses theanode material as the supporting structure. Within the anode structure,a fuel passage 14 and an air passage 20 are provided in opposingrelation. The air channel 20 is lined with an electrolyte layer 28, andthen with a cathode layer 26. Chemical vapor deposition could be used todeposit the internal layers, or by using solutions of viscous pastes.

In FIGS. 40A and 40B, a further embodiment is shown for ananode-supported version of the SOFC Stick™ device 10. In thisembodiment, the separate open fuel passage 14 is eliminated, such thatthe porous anode 24 also serves as the fuel passage 14. In addition, theSOFC Stick™ device 10 is coated with a barrier coating 60, such as aglass coating or a ceramic coating, to prevent the fuel from exiting outthe sides of the device 10. The SOFC Stick™ device 10 may have as manyair passages with associated electrolyte and cathode in the anodestructure as desired. As depicted in FIG. 40B, the fuel from fuel supply34 is forced into first end 11 a through the porous anode 24, whichserves as the fuel passage 14, and passes through the electrolyte layers28 and the cathodes 26 to react with air from air supply 36, and thespent air and fuel can then exit out the air outlet 22.

In another embodiment depicted in a schematic cross-sectional end viewin FIG. 41A and a schematic cross-sectional top view in FIG. 41B, theSOFC Stick™ device 10 may include a plurality of air passages 20provided within the anode-supporting structure, and a single fuelpassage 14 normal to the multiple air passages 20 for feeding fuel fromthe fuel supply 34 through the single fuel inlet 12 to multiple airpassages 20. Again, the air passages 20 are lined first with anelectrolyte layer 28 and then with a cathode 26. The fuel passes fromthe single fuel passage 14 through the anode structure 24, through theelectrolyte 28, and through the cathode 26 to react with the air in theair passage 20, and the spent fuel and air exits from the air outlet 22.The spent fuel can also seep out the side of the SOFC Stick™ device 10that does not include the barrier coating 60, which uncoated side wouldbe located on the opposing side of the device from the orientation ofthe single fuel passage 14.

In the embodiments pertaining to an anode-supported structure, it may beappreciated that the structure may be essentially reversed to be acathode-supported structure. Fuel channels coated with an electrolytelayer and an anode layer would then be provided within the cathodestructure. A separate air channel or multiple air channels could also beprovided, or the porosity of the cathode could be used for the air flow.

FIGS. 42A-42C depict a method for forming the electrodes within the airand fuel passages. Taking the fuel passage 14 and anode 24 as anexample, rather than building up a green structure layer by layer usinglayers of green ceramic and metal tape layers, or printingmetallizations, in the present embodiment, the SOFC Stick™ device 10 isfirst built without the electrodes. In other words, green ceramicmaterial is used to form the electrolyte and ceramic supporting portionsof the SOFC Stick™ and the organic material is used to form thepassages, such as fuel passage 14. After the SOFC Stick™ device has beensintered, the fuel passage 14 is filled with an anode paste or solution.The paste may be thick like that of a printing ink, or runny like thatof a high-content water solution. The anode material can be filled intothe fuel passage 14 by any desired means, such as sucking it in via avacuum, by capillary forces, or forcing it in via air pressure.

Alternatively, as shown in FIGS. 42A-42C, the anode material isdissolved in solution, flowed into the fuel passage 14, and thenprecipitated. For example, through a change of pH, the anode particlescan be precipitated and the solution drawn out. In another alternative,the anode particles can be simply allowed to settle, and then the liquiddried or baked out of the fuel passage 14. This settling can beaccomplished by creating an ink or liquid carrier that will not keep theparticles in suspension for any extended period of time, for example,due to low viscosity. A centrifuge could also be used to force thesettling. The centrifuge can easily allow preferential settling of mostparticles onto one surface of the fuel passage 14 to thereby conserveelectrode material and to ensure that only one surface of the fuelpassage 14 acts as an electrolyte.

As shown in FIG. 42A, the anode particle-containing solution 66 ispulled into the fuel passage 14 until the passage 14 is completelyfilled, as shown in FIG. 42B. The particles then settle to the bottom ofthe passage 14 to form an anode layer 24, as shown in FIG. 42C. Floodingin of the solution 66 can be accelerated by gravity, vacuum, orcentrifuge, as compared to normal capillary forces. Of course, while theanode 24 and fuel passage 14 were used as an example, any of thesealternative embodiments may also be used with a cathode paste orsolution to create a cathode layer 26 in an air passage 20.

In another alternative, a ceramic electrode material (anode or cathode)could be infused into the passage (fuel or air) in a liquid sol-gelstate, and then deposited inside the passage. It is also possible torepeat the filling operation multiple times, such as in the case wherethe concentration of the desired electrode material in the liquid islow, or to provide a gradient of properties in the electrode (such as toprovide a different amount of YSZ in the electrode close to theelectrolyte versus the amount of YSZ in the electrode farther from theelectrolyte), or if there is a desire to put multiple layers ofdissimilar materials together (such as a cathode made of LSM near theelectrolyte, and then silver over the top of the LSM for betterconductivity).

Referring back to FIGS. 7C and 7D, in which ceramic spheres or ballswere used to provide structural support to the air and fuel passages 20,14, ceramic particles may also be used to increase the effective surfacearea for a greater reaction area, thus giving a higher output. Veryfine-sized ceramic balls or particles can be used inside the fuelpassage 14 and the air passage 20 prior to applying the electrode layer.As shown in FIG. 43 in schematic cross-sectional side view, surfaceparticles 62 line the passage 14 to provide the electrolyte layer 28with an uneven topography that increases the surface area available toreceive the electrode layer. The anode 24 is then applied over theuneven topography with the anode material coating all around the surfaceparticles 62 thereby increasing the reaction area.

In an alternative embodiment, depicted in schematic cross-sectional sideview in FIG. 44, the electrolyte layer 28 may be laminated so as toprovide the uneven topography or textured surface layer 64, such as bypressing the green electrolyte layer against a fine grading having aV-shaped pattern, which pattern is then imparted to the electrolytelayer 28. After the electrolyte layer 28 is sintered to solidify theceramic and the textured surface layer 64, the anode layer 24 may thenbe applied, such as by using the backfill process described above inFIGS. 42A-42C, to provide an anode with a high reaction area.

Yet another embodiment of the invention is depicted in FIGS. 45A and45B. FIG. 45A is a schematic top view depicting the air and fuel flowthrough air and fuel passages and the arrangement of the electrodes, andFIG. 45B is a cross-sectional view through the hot zone 32. Along thelength of SOFC Stick™ device 10, the device is divided into a left side80 and a right side 82 with an intermediate or bridging portion 84therebetween. A plurality of air passages 20L extend from the first end11 a of SOFC Stick™ device 10 along the length through the left side 80and exit out the left side 80 adjacent second end 11 b, and a pluralityof air passages 20R extend from first end 11 a along the length throughthe right side 82 and exit the SOFC Stick™ device 10 on the right sideadjacent the second end 11 b. The air passages 20L are offset from theair passages 20R, as best shown in FIG. 45B. A plurality of fuelpassages 14L extend from the second end 11 b of SOFC Stick™ device 10along the length through the left side 80 and exit on the left side 80adjacent first end 11 a, and a plurality of fuel passages 14R extendfrom second end 11 b along the length through the right side 82 and exitthe right side 82 adjacent first end 11 a. The fuel passages 14L areoffset from the fuel passages 14R. In addition, with the exception ofone fuel passage and one air passage, each fuel passage 14L is pairedwith and slightly offset from an air passage 20R and each air passage20L is paired with and slightly offset from a fuel passage 14R. For eachoffset pair of fuel passages 14L and air passages 20R, a metallizationextends along each fuel passage 14L from the left side 80 to the rightside 82, where it then extends along the slightly offset air passage20R. Similarly, for each offset pair of fuel passages 14R and airpassages 20L, a metallization extends along each air passage 20L fromthe left side 80 to the right side 82, where it then extends along theslightly offset fuel passage 14R. The metallization serves as an anode24L or 24R when the metallization extends along a fuel passage 14L or14R, and the metallization serves as a cathode 26L or 26R when themetallization extends along an air passage 20L or 20R. In the bridgingportion 84 of the SOFC Stick™ device 10, where the metallizations do notextend along any air or fuel passage, the metallization simply serves asa bridge 90 between an anode and a cathode. In one embodiment of thepresent invention, the metallization may comprise the same materialalong its length, such that the anode 24L or 24R, the bridge 90 and thecathode 26L or 26R each comprise the same material. For example, themetallizations may each comprise platinum metal, which functions well aseither an anode or a cathode. Alternatively, the metallization maycomprise different materials. For example, the cathodes 26R or 26L maycomprise lanthanum strontium manganite (LSM), while the anodes 24R or24L comprise nickel, NiO, or NiO+YSZ. The bridges 90 may comprisepalladium, platinum, LSM, nickel, NiO, or NiO+YSZ. The present inventioncontemplates any combination or type of materials suitable for use as acathode or an anode, or a bridging material therebetween, and theinvention is not limited to the specific materials identified above.

On one side of the SOFC Stick™ device 10, shown here at the right side82, a fuel channel 14R is provided with an associated anode 24R thatextends to the right edge of the SOFC Stick™ device 10 to provide theexternal exposed anode 25. There is no offset air passage 20L associatedwith this fuel passage 14R, and the anode 24R need not extend into theleft side 80. As depicted in FIG. 45A, an exterior contact pad 44 isapplied over the exposed anode 25 and extends along the length of theSOFC Stick™ device into the cold zone 30. Negative voltage node 38 canthen be connected by wire 42 and solder connection 46 to the contact pad44. The anode 24R could extend, as shown, to the right edge throughoutthe hot zone 32, or could just extend in a small tab portion to reducethe amount of electrode material used. Also, the anode 24R could extendto the right edge of the SOFC Stick™ device 10 along the length of thefuel passage 14R, although such embodiment would involve an unnecessaryuse of electrode material.

Similarly, on the other side of the SOFC Stick™ device 10, shown as theleft side 80, a single air passage 20L is provided with an associatedcathode 26L that extends to the left side of the SOFC Stick™ device 10to form the exposed cathode 27. This air passage 20L is not associatedwith an offset fuel passage 14R, and it is not necessary that thecathode 26L extend to the right side 82. A contact pad 44 may be appliedalong the exterior of the left side 80 of the SOFC Stick™ device 10 fromthe exposed cathode 27 to a cold end 30, where a positive voltage node40 may be connected via wire 42 and solder connection 46 to the contactpad 44.

In FIG. 45B, the single fuel passage 14R and associated anode 24R areshown at the top of the right side 82, while the single air passage 20Land associated cathode 26L are shown at the bottom of the left side 80of the SOFC Stick™ device 10. However, the invention is not limited tothat arrangement. For example, air passage 20L and associated cathode26L could be provided also at the top of device 10 on the left side 80,in a similar offset manner to the single fuel passage 14R and itsassociated anode 24R, but the metallization would not run from the leftside 80 through the bridging portion 84 to the right side 82. Rather,the bridge 90 would be absent such that the anode 24R is electricallyseparated from the cathode 26L. Additional arrangements are contemplatedin which an SOFC Stick™ device 10 may be provided with two unique airpathway stacks and two unique fuel pathway stacks within a single SOFCStick™ device 10, with the cells connected in series. The embodimentdepicted in FIGS. 45A and 45B has an advantage of raising the voltagewithout raising the current, and while maintaining a low resistance.Further, this embodiment provides a high density within the SOFC Stick™device 10.

In FIGS. 46A and 46B, an alternative embodiment is depicted in schematicperspective view and schematic cross-sectional view, respectively.Previous embodiments (e.g., FIG. 37) provided external stripes along theexterior sides or edges of the SOFC Stick™ device 10 from the hot zone32 to the cold zone(s) 30 to provide a path of low resistance for theelectrons to travel to the cold-end. In the embodiment of FIGS. 46A and46B, instead of stripes down the sides or edges of the device 10, acontact pad 44 is applied along one side and one of the top and bottomsurfaces for the external connection to the anode 24 and another contactpad 44 is applied along the opposing side and the other of the top andbottom surfaces for the external connection to the cathode 26. Thus, theelectrons have a large or wide path along which to travel, therebyproviding an even lower resistance. These large conductor pads 44 thatare applied on two adjacent surfaces could be used in any of theembodiments disclosed herein.

In FIG. 47, yet another embodiment is depicted, in schematiccross-sectional side view, of an SOFC Stick™ device 10 that takesadvantage of heat exchange principles. After the heated air and fuelpass through the active zone 33 b of the hot zone 32 (i.e., the portionof the hot zone 32 where the anode 24 is in opposing relation to thecathode 26 with an electrolyte therebetween), the fuel passage 14 andair passage 20 are joined into a single exhaust passage 21. Anyun-reacted fuel will burn when combined with the heated air, thusproducing additional heat. The exhaust passage 21 travels back towardthe cold zone 30 adjacent the active zone 33 b, with the direction offlow of the exhaust (spent fuel and air) being opposite that of theincoming fuel and air in the adjacent fuel and air passages 14, 20. Theadditional heat generated in the exhaust passage 21 is transferred tothe adjacent passages 14, 20 to heat the incoming fuel and air.

FIGS. 48A-48C depict an “end-rolled SOFC Stick™ device” 400 having athick portion 402 having a greater thickness than a thin portion 404, asdepicted in FIG. 48A. The fuel and air inlets 12, 18 are positionedadjacent first end 11 a, which is at the end of thick portion 402, andwhile not shown, the air and fuel outlets (16, 22) may be provided atthe sides of the device 400 adjacent opposing second end 11 b, which isat the end of the thin portion 404. The thick portion 402 should bethick enough to provide mechanical strength. This may be achieved byproviding thick ceramic 29 around the adjacent fuel and air inlets 12,18. The thin portion 404 will include the active zone 33 b (not shown)that includes an anode (not shown) in opposing relation to a cathode(not shown) with an electrolyte (not shown) therebetween (as in priorembodiments). The thin portion 404 should be thin enough to permit it tobe rolled while in the green (unfired) state, as shown in FIG. 48B.After the thin portion 404 is rolled to a desired tightness, the device400 is fired. The rolled thin portion 404 can then be heated to causethe reaction, while the thick portion 402 is a cold end, as discussed inother embodiments. The end-rolled SOFC Stick™ device 400 is a largesurface area device that can fit in a small space by virtue of rollingthe thin portion 404. Moreover, the thin cross-section of the activezone (33 b) in the thin portion 404 reduces the heat transfer out alongthe ceramic and allows good temperature cycle performance.

While the invention has been illustrated by the description of one ormore embodiments thereof, and while the embodiments have been describedin considerable detail, they are not intended to restrict or in any waylimit the scope of the appended claims to such detail. Additionaladvantages and modifications will readily appear to those skilled in theart. The invention in its broader aspects is therefore not limited tothe specific details, representative apparatus and method andillustrative examples shown and described. Accordingly, departures maybe made from such details without departing from the scope of thegeneral inventive concept.

1. A solid oxide fuel cell device comprising: an elongate ceramicsubstrate having an exterior surface defining an interior ceramicsupport structure having a first non-active end region adjacent a firstend, a second non-active end region adjacent a second end, and an activezone between the first and second non-active end regions, wherein theactive zone comprises an anode and a cathode in opposing relation withan electrolyte therebetween for undergoing a fuel cell reaction whensupplied with heat, fuel and oxidizer, and the first and secondnon-active end regions lack the anode and cathode in opposing relationand extend away from the active zone without being heated to dissipateheat and to thereby remain at a lower temperature than the active zonewhen the active zone is supplied with heat; a fuel inlet in the firstnon-active end region for receiving the supply of fuel and a respectivefuel outlet in at least one of the active zone or the second non-activeend region, the fuel inlet and the fuel outlet coupled therebetween byan elongate fuel passage at least partially extending through the activezone within the interior ceramic support structure, wherein the anode isadjacent the fuel passage in the active zone within the interior ceramicsupport structure and electrically connected from within the interiorceramic support structure to a first exterior contact surface on theexterior surface of the elongate ceramic substrate in at least one ofthe first or second non-active end regions for external connection to anegative voltage node; and an oxidizer inlet in the second non-activeend region for receiving the supply of oxidizer and a respectiveoxidizer outlet in at least one of the active zone or the firstnon-active end region, the oxidizer inlet and the oxidizer outletcoupled therebetween by an elongate oxidizer passage at least partiallyextending through the active zone within the interior ceramic supportstructure in opposing relation to the elongate fuel passage, wherein thecathode is adjacent the oxidizer passage in the active zone within theinterior ceramic support structure and electrically connected fromwithin the interior ceramic support structure to a second exteriorcontact surface on the exterior surface of the elongate ceramicsubstrate in at least one of the first or second non-active end regionsfor external connection to a positive voltage node, wherein theelectrolyte is a ceramic co-fired with the interior ceramic supportstructure.
 2. The fuel cell device of claim 1 wherein a length betweenthe first end and the second end is at least 5 times greater than awidth and a thickness of the elongate ceramic substrate whereby theelongate ceramic substrate exhibits thermal expansion along a dominantaxis that is coextensive with the length.
 3. The fuel cell device ofclaim 1 wherein the fuel outlet is in the active zone adjacent thesecond non-active end region.
 4. The fuel cell device of claim 1 whereinthe fuel outlet is in the second non-active end region adjacent thesecond end.
 5. The fuel cell device of claim 1 wherein the oxidizeroutlet is in the active zone adjacent the first non-active end region.6. The fuel cell device of claim 1 wherein the oxidizer outlet is in thefirst non-active end region adjacent the first end.
 7. The fuel celldevice of claim 1 wherein the elongate ceramic substrate includes: afirst elongate portion containing the first non-active end region anddefined by a length between the first end and the active zone and awidth transverse thereto, a second elongate portion containing thesecond non-active end region and defined by a length between the secondend and the active zone and a width transverse thereto, and a centralsection containing the active zone and defined by a length and a width,wherein the lengths of the first and second elongate portions are atleast 5 times greater than the widths and a thickness of the elongateceramic substrate in the respective first and second elongate portionssuch that the first and second elongate portions each exhibit thermalexpansion along a dominant axis that is coextensive with the respectivelengths, and wherein the length and width of the central section are notsubstantially different such that the central section exhibits thermalexpansion along a first axis that is coextensive with the length andalong a second axis that is coextensive with the width.
 8. The fuel celldevice of claim 7 wherein the fuel outlet is in the active zone adjacentthe second non-active end region and the oxidizer outlet is in theactive zone adjacent the first non-active end region.
 9. The fuel celldevice of claim 7 wherein the fuel outlet is in the second non-activeend region adjacent the second end and the oxidizer outlet is in thefirst non-active end region adjacent the first end.
 10. The fuel celldevice of claim 1 wherein the fuel outlet is in the active zone adjacentthe second non-active end region and the oxidizer outlet is in theactive zone adjacent the first non-active end region.
 11. The fuel celldevice of claim 1 wherein the fuel outlet is in the second non-activeend region adjacent the second end and the oxidizer outlet is in thefirst non-active end region adjacent the first end.
 12. The fuel celldevice of claim 1, further comprising a negative voltage connection tothe first exterior contact surface, and a positive voltage connection tothe second exterior contact surface.
 13. A solid oxide fuel cell systemcomprising: a hot zone chamber; a plurality of the solid oxide fuel celldevices of claim 1, each positioned with the respective active zones ofeach solid oxide fuel cell device in the hot zone chamber and therespective first and second non-active end regions of each solid oxidefuel cell device extending outside the hot zone chamber; a heat sourcecoupled to the hot zone chamber and adapted to supply the heat to theactive zones within the hot zone chamber; a fuel supply coupled outsidethe hot zone chamber to the first non-active end regions in fluidcommunication with the fuel passages for supplying the fuel into thefuel passages; an air supply coupled outside the hot zone chamber to thesecond non-active end regions in fluid communication with the oxidizerpassages for supplying the oxidizer into the oxidizer passages; anegative voltage connection to the first exterior contact surfacesoutside the hot zone chamber; and a positive voltage connection to thesecond exterior contact surfaces outside the hot zone chamber.
 14. Thefuel cell system of claim 13 wherein a length between the first ends andthe second ends is at least 5 times greater than a width and thicknessof the elongate ceramic substrate whereby the elongate ceramic substrateexhibits thermal expansion along a dominant axis that is coextensivewith the length.
 15. The fuel cell system of claim 13 wherein the fueloutlet is in the active zone adjacent the second non-active end regionand the oxidizer outlet is in the active zone adjacent the firstnon-active end region.
 16. The fuel cell system of claim 13 wherein thefuel outlet is in the second non-active end region adjacent the secondend and the oxidizer outlet is in the first non-active end regionadjacent the first end.
 17. A method of using the device of claim 1,comprising: positioning the elongate ceramic substrate with the activezone in a hot zone chamber and the first and second non-active endregions extending outside the hot zone chamber; coupling a fuel supplyoutside the hot zone chamber to the first non-active end region so thatit is in fluid communication with the fuel inlet; coupling an air supplyoutside the hot zone chamber to the second non-active end region so thatit is in fluid communication with the oxidizer inlet; connecting anegative voltage to the first exterior contact surface; connecting apositive voltage to the second exterior contact surface; applying heatin the hot zone chamber to heat the active zone to a temperature above400° C. while maintaining the first and second non-active end regions ata temperature less than 300° C.; supplying fuel and air through therespective fuel and oxidizer inlets to the respective fuel and oxidizerpassages in the heated active zone whereby the fuel and air react andproduce electrons that travel to the respective first and secondexterior contact surface and between the negative and positive voltageconnections.
 18. The method of claim 17, wherein applying heat is toheat the active zone to a temperature above 700° C.
 19. A method ofusing the system of claim 13, comprising: applying heat in the hot zonechamber to heat the active zones to a temperature above 400° C. whilemaintaining the first and second non-active end regions at a temperatureless than 300° C.; supplying fuel and air from the respective fuel andair supplies into the respective fuel and oxidizer passages to theheated active zone to react the fuel and air and produce electrons thattravel to the respective first and second exterior contact surfaces andbetween the negative and positive voltage connections.
 20. The method ofclaim 19, wherein applying heat is to heat the active zones to atemperature above 700° C.